1. Field of the Invention
The invention relates to a method of removing a thin metallic layer during manufacture of thin film devices such as magnetic recording heads; and, specifically the invention relates to an etchant solution and method of use for removing a thin metallic layer.
2. Description of the Background Art
In many thin film devices a metal layer is formed on an insulating substrate by first depositing a thin metallic layer such as a conductive seed layer. A patterned layer of photoresist is then formed following by electrodeposition. Typically, the photoresist is removed and a second photoresist layer is formed which protects the desired portions of the electrodeposited material. An etchant is then used to remove exposed portions of the thin metallic layer.
An example is the fabrication of a thin film magnetic recording head. In this example, the magnetic poles of the inductive write head and the copper turns in the write head are created with the method outlined above.
Frame plating is typically used in the construction of electrodeposited structures. Briefly, after the deposition of a thin metallic layer, a first layer of photoresist is formed. The first layer of photoresist is thicker than the desired final electrodeposited feature and is formed as a frame of several microns surrounding the final desired features. The desired metal is electrodeposited through the patterned first layer of photoresist within the frame. The desired metal is also typically plated simultaneously outside the frame to form a field. By plating both the desired features within the frame and the field outside the frame, good uniformity and composition control of the electroplated features is achieved. The first layer of photoresist is then removed and a second layer of photoresist is formed and patterned to protect the desired electroplated features while simultaneously leaving the field material exposed to subsequent etching. An etchant solution is then used to remove the exposed thin metallic layer and the exposed field material. The lateral etch rate is subject to factors which are difficult to control such as film stress and varying surface energy of the interfaces. Consequently, conventional chemical etchants may exhibit greater lateral etching rates compared with etching normal to the thin metallic layer. The higher lateral etch rates may enable the etchant solution to attack the material under the protective photoresist resulting in undercutting. Due to the visual appearance, the damage due to high lateral etching rates is sometimes called rat bites. In severe cases of rat bites the chemical etchant may damage the protected electrodeposited material.
To solve these problems, a chemical etchant solution and method of use is needed which eliminates or greatly reduces the rat bite problem.